1. Field of the Invention
This invention relates generally to perpendicular magnetic recording media, and more particularly to a disk with a perpendicular magnetic recording layer for use in magnetic recording hard disk drives.
2. Description of the Related Art
Perpendicular magnetic recording, wherein the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer, is a promising path toward ultra-high recording densities in magnetic recording hard disk drives. The most common type of perpendicular magnetic recording system is one that uses a “probe” or single pole recording head with a “dual-layer” media as the recording disk. The dual-layer media comprises a perpendicular magnetic data recording layer (RL) formed on a “soft” or relatively low-coercivity magnetically permeable underlayer (SUL), with the SUL serving as a flux return path for the field from the pole recording head. This type of system is also called “Type 1” perpendicular magnetic recording. A schematic of such a prior art system with a read element for reading the recorded data is shown in FIG. 1.
FIG. 2 is a schematic of a cross-section of a prior art perpendicular magnetic recording disk showing the write field H acting on the recording layer RL. The disk also includes the hard disk substrate, a seed or onset layer (OL) for growth of the SUL, an exchange break layer (EBL) to break the magnetic exchange coupling between the magnetically permeable films of the SUL and the RL and to facilitate epitaxial growth of the RL, and a protective overcoat (OC). As shown in FIG. 2, the RL is located inside the gap of the “apparent” recording head (ARH), which allows for significantly higher write fields compared to longitudinal or in-plane recording. The ARH comprises the write pole (FIG. 1) which is the real write head (RWH) above the disk, and a secondary write pole (SWP) beneath the RL. The SWP is facilitated by the SUL, which is decoupled from the RL by the EBL and produces a magnetic mirror image of the RWH during the write process. This effectively brings the RL into the gap of the ARH and allows for a large write field H inside the RL. However, this geometry also results in the write field H inside the RL being oriented nearly parallel to the surface normal, i.e., along the perpendicular easy axis of the RL grains, as shown by typical grain 10 with easy axis 12. The parallel alignment of the write field H and the RL easy axis has the disadvantage that relatively high write fields are necessary to reverse the magnetization because no torque is exerted onto the grain magnetization. Also, a write-field/easy-axis alignment increases the magnetization reversal time of the RL grains (M. Benakli et al., IEEE Trans. MAG 37, 1564(2001)). For these reasons, “tilted” media have been theoretically proposed, in which the magnetic easy axis of the RL is tilted at an angle of about 45 degrees with respect to the surface normal, so that magnetization reversal can be accomplished with a lower write field and without an increase in the reversal time. (K.-Z. Gao and H. N. Bertram, IEEE Trans. MAG 39, 704(2003)). However, there is no known fabrication process to make high-quality recording media with a tilted easy axis.
What is needed is a perpendicular magnetic recording media that displays a magnetization reversal behavior similar to tilted media and is fully compatible with conventional fabrication processes.